Observation of the Wind
At the time of the Ring of Fire, the characters will not know the average speed of the wind, as no devices for that purpose had yet been invented. The wind will be described in qualitative terms. Smith's Sea Grammar (1627) classified the wind level as stark calm, calm, fresh gale, loome gale, stiff gale, storm, tempest, and "hericano"; note that "gale" was then a generic term for a wind, and "breeze" was used only along the coast, in the context of a "land breeze" or "sea breeze." (Huler 85).
In 1806, Beaufort proposed standardization of the British Navy's wind descriptions in log entries, characterizing the wind force in terms of how much sail a sailing ship may safely carry, and his scale was mandated by the Admiralty in 1838. In 1906, the scale was recast, for the benefit of steamships, in terms of sea state.
The first anemometer was one in which the wind caused a hinged, hanging plate to be deflected from the vertical; this was described by Leon Battista Alberti in 1450 (Huler 189). Unfortunately, swinging plate anemometers aren't accurate at sea, because of the motion of the ship. Still, one was carried on a Swedish warship in 1779 (89). The more practical cup anemometer was invented in 1846 (191). There is probably an exemplar at the high school science department in Grantville.
A variety of anemometers are described in the Grantville encyclopedias, and possibly in other Grantville literature (Popular Science back issues, Amateur Scientist column in Scientific American, science fair project books) and it's reasonably likely that at least the Science Department at the school has basic weather equipment such as a barometer, a thermometer and a anemometer mounted on the rooftop. Indeed, it probably has a combination barograph-thermograph for recording pressure and temperature.
So, within a year or two after the RoF, it's possible that anemometers have been built, and governments could require their use on shipboard to record wind information for the ship's log.
Each year, as the logbooks were turned in and analyzed, you would refine the body of wind climatology data for the standard sailing routes. Ideally, you would collect wind data for at least thirty years, the standard period for computation of climatological norms.
****
While the broader development of meteorology is outside the focus of this article, this author thinks it likely that crude but serviceable thermometers, barometers and anemometers will be manufactured within a few years after RoF, and purchased by governments, nobles, professionals, merchants and the military throughout Europe.
Inevitably, meteorological records will be kept, and this will lead in turn to meteorological reports and even forecasts in the newspapers and on the radio and telegraph. In eighteenth-century Europe, informal networks of towns shared weather observations (De Villiers 133), and by the 1840s, weather events were telegraphed across regions of the United States and Britain. (Monmonier, 40).
In Flint, 1633, Chapter 14, Jesse tells Jim, "We need someone to organize a weather service. . . ." In October 1633, the Voice of America, broadcasting from Grantville, features a "local weather forecast." Hughes, "Turn Your Radio on, Episode Two" (Grantville Gazette 20).
I imagine that the weather was mentioned on the weekly Farm-to-Market report mentioned in Huff and Goodlett, "Waves of Change" (Grantville Gazette 9).
Merton Smith of TransEuropean Airlines calls up the weather service in Huff and Goodlett, "High Road to Venice," and he has weather information from as far away as Rome. (Grantville Gazette 19). By fall, 1635, there are weather stations in Russia, at least one of which is equipped with an up-time thermometer and barometer, although their data is transmitted by messenger rather than by radio. Huff and Goodlett, "Butterflies in the Kremlin, Part Seven, The Bureaucrats are Revolting" (Grantville Gazette 9).
Thus, we anticipate that the characters will combine their qualitative knowledge of the winds that prevailed before the Ring of Fire, with the limited quantitative information that the Grantville literature furnishes on late-twentieth century wind climatology, and use it to predict the prevailing winds that will be experienced in the decades following the Ring of Fire.
Winds Aloft
As you go higher, air temperature and pressure drop, at least until you reach 11 km. Upper air weather maps often are identified in terms of the standard pressure at the height the measurements were made, rather than the height (above sea level) directly. Note that one millibar (mb) equals 100 pascals. The weather maps most often available are for the "pressure altitudes" shown below:
Winds increase in speed with altitude, because they aren't slowed down as much by friction with the earth's surface. I assume an exponential increase in wind speed with height, with the reference height being 10 meters (standard meteorological practice) and the exponent being 0.2. The exponent in fact depends on the terrain below, and the stability of the air, and you can find a list of suitable values for different circumstances at
http://en.wikipedia.org/wiki/Wind_gradient
Winds also change direction with altitude, either veering (turning clockwise with height) or backing (turning counter-clockwise). Generally speaking, they veer in the northern hemisphere and back in the southern, because the upper air levels experience less "frictional" drag than the lower ones and thus the wind is faster, and this means that the Coriolis force, which is perpendicular to the wind and proportional to the wind speed, is greater. Here's an applet to play with:
http://itg1.meteor.wisc.edu/wxwise/kinematics/testwind2.html
However, veering and backing can also occur as a result of horizontal temperature gradients ("thermal wind") so it's a complex matter. The matter is alluded to by McGHEST/"Wind."
Over the ocean, the average veering is 10.5° at 1,000 meters height (relative to the surface wind), and rising another 1,000 meters adds another 2.5°. (Gray 49). The effects of latitude (0-60°), wind speed and season are minor, with, at 1,000 meters height, perhaps a 4° range (Gray 49, 51, 54). Over land, the veer at 1,000 meters is much larger, perhaps 25-35°. (Gray 75-6).
****
There's a weather proverb, "If clouds move against the wind, rain will follow." It's evidence of wind shear, wind direction aloft being different than wind direction at the surface. (So, too, is the movement of different cloud layers in different directions at the same time.) I am not sure how old the saying is, but I found it in Loudon's 1824 Encyclopaedia of Gardening. The down-timers are much more familiar with the outdoors than we are, and may have noticed this phenomenon. Certainly, ships' officers may be asked to note any evidence of wind shear in the future.
There is limited information in Grantville Literature about winds aloft. The EB2002CD essays on monsoons set forth the vertical thickness of the monsoon zone. EB2002CD also mentions the "antitrade wind," a "steady wind that blows poleward and eastward between latitudes 30° N and 30° S, at altitudes of 2 to 12 kilometres (about 1 to 7 miles). Such winds overlie the westward-blowing trade winds." So, if a transatlantic airship could cruise at an altitude of 2 kilometers or higher, it could take advantage of the antitrades to retrace its steps, if that would be more convenient than jogging northward to the westerlies.